1. Field of the Invention
The present invention relates to a digital TV and more particularly to an apparatus and method for converting a picture scanned in the interlaced scanning pattern to a picture scanned in the progressive scanning pattern.
2. Discussion of Related Art
Generally, a picture of a digital TV may be scanned on a monitor by an interlaced scanning pattern or a progressive scanning pattern. Some display monitors requires one type of scanning pattern while the picture is received in another type of scanning pattern. A deinterlacing apparatus is used to convert a picture scanned in the interlaced scanning pattern to a picture scanned in the progressive scanning pattern, filling the pixel value omitted in one field to provide a perfect frame.
For example, a deinterlacing apparatus is required to display TV signals on the monitor of a computer. Because the computer monitor supports the progressive scanning system and the TV signal such as NTSC supports the interlaced scanning system, the TV signal of the interlaced scanning system must be converted to signals in the progressive scanning system in order to view the picture on the computer monitor.
To fill the pixel values omitted in a field and complete one frame, the deinterlacing apparatus and method employs interpolation in the field, interpolation in the field or compensation between the fields through motion detection, or compensation between the fields using motion vectors through motion estimation. A deinterlacing apparatus and method employing interpolation in just the field is used for a very simple system.
FIGS. 1a through 1c are diagrams illustrating a grand-alliance deinterlacing procedure according to prior art, in which the grand-alliance deinterlacing procedure is adopted to perform interpolation in the field and compensation between the fields by way of motion detection. FIGS. 2a and 2b illustrate a deinterlacing procedure employing motion compensation according to the prior art, in which the deinterlacing procedure is adapted to perform compensation between the fields using motion vectors via motion estimation.
In the deinterlacing procedure employing motion detection recommended by the HDTV standards of the North American area, pixels A to H adjacent a pixel to be filled are determined as shown in FIG. 1b. The location of these pixels are used to calculate E1=.vertline.F-C.vertline., E2=.vertline.(D+E)/2-(A+B)/2.vertline. and E3=.vertline.(D+E)/2-(G+H)/2.vertline.. The largest one of the values E1, E2 and E3 is set to E.sub.max for motion detection. The value of E.sub.max is then compared with thresholds T1 and T2 to determine the value of .varies., as shown in FIG. 1c, in which .varies. is the weight for interpolation in the field and 1-.varies. is the weight for compensation between the fields. After determining the weights for interpolation in the field and compensation between fields, the value of the omitted pixel as shown in FIG. 1a is calculated as ((D+E)/2)*.varies.+C*(1-.varies.) and other omitted pixels are also filled in a similar way.
The deinterlacing apparatus employing interpolation in both the field and compensation between the fields provides progressive pictures of high quality relative to a deinterlacing apparatus that performs interpolation in just the field. However, it is difficult to determine the thresholds values T1 and T2 used to calculate the weights for interpolation in the field and compensation between the fields.
If the threshold T1 has an extremely small value, the interpolation in the field prevails over compensation between the fields and does not achieve a high quality picture. On the contrary, a too large threshold T2 makes the compensation between the fields prevail over the interpolation in the field. The heavy weight in the compensation between the fields may be better for a still picture, but performs interpolation with erroneous pixel values for a moving picture causing deterioration of picture quality.
FIGS. 2a and 2b shows a deinterlacing procedure using motion vectors to perform compensation between the fields via motion estimation. As shown, a motion estimating section 21 searches for motion of an input picture to determine the pixels most likely omitted from pixels A to L, and a deinterlacing section 22 fills the omitted pixels with pixels indicated by the motion vector.
However, a picture produced by a deinterlacing procedure using motion vectors has much errors in the motion estimation due to its poor vertical resolution. Also, the motion estimating procedure is extremely complex, requiring many calculations in the deinterlacing section 22, which raises the cost of filling the omitted pixels.